Effect of surface acidity of cyano-bridged polynuclear metal complexes on the catalytic activity for the hydrolysis of organophosphates

Heterogeneous catalysis of cyano-bridged polynuclear metal complexes, which were prepared by systematic replacement of C-bound metal ions (M-C) and/or N-bound metal ions (M-N) of Prussian blue ([M-N(H2O)(x)](y)[Fe-II/III(CN)(6)]; M-N = Fe-III, Ga-III, Mn-II, Zn-II or Co-II: [Fe-II/III(H2O)(x)](y)[M-C(CN)(6)]; M-C = Fe-II, Pt-IV, Co-III, Ir-III or Ru-II), was examined for the hydrolysis of p-nitrophenol phosphate (p-NPP) as a model compound of insecticides. The catalytic activity of the complexes was enhanced by employing metal ions in higher oxidation states at the C- and N-bound sites, although only N-bound metal ions act as active sites. The dependence of the initial reaction rates for the hydrolysis on the initial concentration of p-NPP suggested that the rate determining step is the adsorption of p-NPP onto catalyst surfaces. The surface acidity of each complex estimated by the heat of pyridine desorption is strongly correlated with catalytic activity.